DAC (Dedicated Administrator Connection) is a well-known function of SQL Server for the case that the server isn’t responding to regular connection for various reasons like heavy-load etc. Having the magic DAC in the pocket can lead administrators to the opinion that they are save in such a case, that they will simply connect and do all the rescue jobs, i.e. backup critical databases and restore them to another server. But’ that thinking only means that they have forgotten one core limitation the DAC has.
The DAC connection doesn’t support parallel executed operations like BACKUP and RESTORE are. This means, the when the server isn’t responding to regular connections we can’t simply connect to it via DAC and make backups of the critical databases when necessary. If we will try to run BACKUP from it, the following error message will appear:
There is not much more to say. Simply remember it as a crucial limitation when you will think about your disaster recovery plans.